including a class template within a map

I have a template class Test, and I am trying to define the following function in a separate header file:

template<typename T>
T dtest(const int, std::map<int, Test<T> >& y);

but I get the following error:

‘Test’ was not declared in this scope

template argument 2 is invalid

开发者_Python百科

template argument 4 is invalid

Given that you assert that the header that defines Test<T> is included by the header that declares dtest, I'm going to guess you have a circular include: The Test<T> header also includes the dtest header.

#include <map>
template<class T>
class Test{};

template<typename T>
T dtest(const int, std::map<int, Test<T> >& y);

This compiles fine so as long as you include the definition of Test and map; the code is fine.